2006 GMC Envoy Owner's Manual - Page 13

{CAUTION: Sitting in a reclined position when your vehicle is in motion can be dangerous. Even if you buckle up, your safety belts cannot do their job when you are reclined like this. The shoulder belt cannot do its job. In a crash, you could go into it, receiving neck or other injuries. The lap belt cannot do its job either. In a crash the belt could go up over your abdomen. The belt forces would be there, not at your pelvic bones. This could cause serious internal injuries. For proper protection when the vehicle is in motion, have the seatback upright. Then sit well back in the seat and wear your safety belt properly. Do not have a seatback reclined if your vehicle is moving. 1-7